1. Field of the Invention
The present invention is generally directed to a method of impeding the evaporation of organic solvents including fuels by using an oligomeric or polymeric materials dissolved in the solvent. Other aspects of this invention include a method of storing solvents while minimizing the evaporation of the solvent and the composition of the solvent/oligomer or the solvent/polymer mixture.
2. Background
Over the past few years there has been an increasing public awareness of environmental issues in particular air pollution. In even the smallest of cities and towns, air pollution is of concern to government officials because of its detrimental effects on health and quality of life. Smog is especially troublesome. Smog and smog-like toxins are generated when admixtures of nitric oxides, (NO.sub.x) and volatile organic compounds (VOCs), such as aliphatic and aromatic hydrocarbons, ethers, ketones, aldehydes etc. are exposed to sunlight. The principle source of NO.sub.x is automobile exhaust although industrial and residential boilers and water heaters also contribute. Volatile organic compounds are generated by either incomplete combustion or evaporation of volatile liquids such as gasoline, diesel fuel, fuel oil, charcoal fluid, paint and lacquer thinner, cleaning solvents, non-detergent degreasers, etc. In many large metropolitan areas, special ordinances restricting use or handling and storage of liquids that form VOCs have been enacted and enforced. This in turn has caused the development of devices and technologies that contain or limit the release of VOCs into the air.
In addition, as a result of cost-prohibitive technological underdevelopment the petroleum industry has for many years known and grudgingly accepted the evaporation of gasoline, diesel fuel, kerosene, aviation fuel, etc. in these under-developed countries or remote regions of the world where such liquids are stored and used. Typically storage of even moderate amounts of these volatile liquids occurs in open or directly vented containers out of which a substantial portion of the liquid evaporates. Not only is the generation of VOCs of environmental concern, but the evaporation of the liquids adds to the cost of shipping, handling, storage and end use of these products.
A number of devices and technologies have been developed that reduce or contain the VOCs generated by the evaporation of volatile liquids. Examples include ventless storage tanks, and vapor recovery systems such as those used in automobile service stations, as well as industrial systems that cool the liquid or place a "cap" of inert or some other pressurized gas over the surface of the liquid. While effective, such systems are expensive to build and maintain and add to the difficulty of storage, transportation and transfer of the liquid. The cost of these technologies is too great for use in under-developed countries or remote locations. Thus there remains an unmet need for an inexpensive, simple method of impeding the evaporation of volatile liquids.
One such method and a composition useful carrying out that method is described by Canevari in U.S. Pat. Nos. 4,326,986 and 4,386,052. In the practice of the Canevari method, a mixture of a surfactant and an alkyl polyol is applied to the surface of crude oil, or other hydrocarbon liquid, so as to form a physical layer or thin film on the surface of the exposed surface of the liquid. Canevari characterizes the thin film being most effective when greater than 70 monolayers and preferably 210 to 350 monolayers thick on the surface. The mixture itself consists essentially of a surfactant, such as a commercially available foaming agent, which is not soluble in hydrocarbons and a polyol having a molecular weight between 100 and 1200 AMU, such as ethylene glycol. Ideally the mixture is applied to the crude oil surface by spraying or aerosolizing techniques to form the physical layer. Although not addressed by Canevari, it is reasonable to conclude that after transferring the liquid to a new container, the surface of the liquid in the new container must be re-treated to again minimize evaporation.